Naci Görür

An abrupt drowning of the Black Sea shelf

Abstract During latest Quaternary glaciation, the Black Sea became a giant freshwater lake. The surface of this lake drew down to levels more than 100 m below its outlet. When the Mediterranean rose to the Bosporus sill at 7,150 yr BP 1 , saltwater poured through this spillway to refill the lake and submerge, catastrophically, more than 100,000 km2 of its exposed continental shelf. The permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of Europe at that time.

Kinematic history of the opening of the Black Sea and its effect on the surrounding regions

The Black Sea consists of two oceanic basins separated by the mid-Black Sea ridge. The east-west-oriented west Black Sea basin opened as a back-arc rift in the Cretaceous by tearing a Hercynian continental sliver, the Istanbul zone, from the present-day Odessa shelf. The Istanbul zone, which was initially contiguous with the Moesian platform in the west, moved south during the Late Cretaceous-Paleocene with respect to the Odessa shelf along two transform faults: the dextral west Black Sea and the sinistral west Crimean faults. It collided in the early Eocene with a Cimmeride zone in the south, thereby ending the extension in the western Black Sea and deactivating both the west Black Sea and the west Crimean faults as strike-slip faults. The east Black Sea basin opened as a result of the counterclockwise rotation of an east Black Sea block around a rotation pole located north of the Crimea. This block was bounded by the west Crimean fault, the southern margin of the eastern Black Sea, and the southern frontal thrusts of the Greater Caucasus. The rotation of the east Black Sea block was contemporaneous with the rifting of the west Black Sea basin but lasted until the Miocene, resulting in continuous compression along the Greater Caucasus.

Tectonic Evolution of the Central Anatolian Basins

The central Anatolian basins can be grouped into two basic types—arc-related (forearc and intra-arc) basins and collision-related (peripheral foreland) basins. The former began developing in the Late Cretaceous, whereas the latter started to form at the beginning of the Eocene. Both types of basins were filled until the Oligocene with turbidites overlain by shelf and nonmarine strata. During the Oligocene, all these basins were unified into a large epi-Anatolide molasse basin, in which widespread gypsiferous series were deposited together with abundant clastic deposits and volcanics. After the Oligocene, these basins evolved into an areally more extensive “intra-cratonic” basin that bears no relation to the earlier orogenic structures. This superposition of different types of basins makes the geology of central Anatolia extremely complicated. To date, no reliable evolutionary tectonic model for this region has been formulated. Considering that the hydrocarbon potential of these basins is largely unknown, ...

Timing of opening of the Black Sea basin

Abstract A detailed study of the Mesozoic palaeogeographic evolution of the Rhodope-Pontide fragment and the region surrounding the Black Sea as a whole shows that the Black Sea basin began opening as a back-arc basin by the rifting of a young continental margin magmatic arc during Aptian-Cenomanian time. During the early Cretaceous the present Black Sea region was occupied by an extensive, generally south-sloping, shallow, carbonate-dominated shelf developed in the late Jurassic along the south-facing Atlantic-type continental margin of Eurasia north of the Neo-Tethys. Following the onset of subduction-related volcanism on the Rhodope-Pontide fragment in the Aptian-Albian, disintegration of this shelf started in the Western Pontides and in the Moesic platform. Block-faulting and accompanying subsidence accelerated in the Cenomanian and in a number of places (e.g. the Rhodope-Pontide fragment, Pre-Caucasus, Crimea, Moldavia) caused the formation of large depressions or basins on the subsided blocks with deposition of deeper water sediments locally intercalated with volcanics. This Cenomanian disintegration, which began tearing the Rhodope-Pontide fragment from the main Eurasian continental block along the young volcanic axis of the south-facing Neo-Tethyan magmatic arc, is here interpreted as the initial rifting and opening of the Black Sea basin, which underwent a uniform, probably thermally-induced, subsidence later in the Senonian. Data from the circum-Black Sea region show that the Black Sea basin is unrelated to the basin opening and closing events in the Caucasus and in the Balkans that occurred in the Jurassic to early Cretaceous.

Origin of the Sea of Marmara as Deduced from Neogene to Quaternary Paleogeographic Evolution of its Frame

The Sea of Marmara Basin (SMB) is connected to the fully marine Mediterranean by the Dardanelles strait and to the brackish Black Sea by the Thracian Bosporus. This linkage to two different marine realms with contrasting water chemistry has been a prime control on the sedimentary history of the SMB, which in turn was controlled by its tectonics. Isolation from any of these realms resulted in drastic changes in its paleoceanographic conditions and made it a part either of the global ocean system or of a brackish-marine environment, depending on the realm from which the connection was severed. The SMB represents the inundated part of the northwestern Anatolian graben system that resulted from the interaction between the North Anatolian fault (NAF) zone and the present N-S extensional tectonic regime of the Aegean. The geologic history of this basin began during the late Serravallian when the NAF was initiated. The first inundation of the basin coincided in both time and space with this initiation. The invad...

Deep structure of the Mid Black Sea High (offshore Turkey) imaged by multi-channel seismic survey (BLACKSIS cruise),

Abstract The Black Sea is considered to be a Mesozoic–Early Cenozoic marginal basin related to the north-dipping subduction of Tethys beneath Europe. However deformation of this basin during the successive Eocene to Neogene collisions of African-derived continental fragments (Kirshehir and Arabian micro plates) remains poorly understood. A multi-channel seismic survey conducted in the central part of the Black Sea has shed light on the superimposed tectonic fabrics of the Central Ridge (the Mid Black Sea High, MBSH) in response to these successive collisions. The MBSH is formed by a series of large NW–SE trending anticlines and synclines, and possible northeast-verging thrusts were identified at the boundary with the deep East Black Sea Basin northeast of the ridge. These buried folds and thrusts, blanketed by 3 to 8 s TWT of undeformed sediments, are interpreted as the offshore extension of the Early Cenozoic tectonic belt resulting from the collision between the Pontides in the north and the Kirshehir block to the south. The offshore part of the belt forming the ridge could have then collapsed when collision ended. Neogene structures also affect the MBSH. A recent graben (the Sinop Trough) extends between this central high and mainland Turkey. This graben could have been formed during the late Miocene incipient dextral strike slip motion of the North Anatolian Fault that was initiated during extrusion of the Anatolian microplate. Active tectonic inversion of deep-seated normal faults present along the Pontides passive margin was also observed along the northeastern flank of the Eastern Pontides. This deformation is the westernmost extension of the Lesser Caucasus front that outlines the suturing of the Eastern Black Sea Basin in easternmost Turkey and in Georgia.

Exploring submarine earthquake geology in the Marmara Sea

The disastrous 1999 earthquakes in Turkey have spurred the international community to study the geometry and behavior of the North Anatolian Fault (NAF) beneath the Marmara Sea. While the area is considered mature for a large earthquake, the detailed fault geometry below the Marmara Sea is uncertain, and this prevents a realistic assessment of seismic hazards in the highly-populated region close to Istanbul. Two geological/geophysical surveys were recently conducted in the Marmara Sea: the first in November 2000 with the R/V Odin Finder, and the second in June 2001 with the R/V CNR-Urania. Both were sponsored and organized by the Institute of Marine Geology of the Italian National Research Council (CNR), in cooperation with the Turkish Council for Scientific and Technical Research (TUBITAK) and the Lamont-Doherty Earth Observatory of Columbia University Multi-beam bathymetry, multi-channel seismic reflection profiling, magnetometry high-resolution CHIRP sub-bottom profiling, and bottom imaging were carried out with a remotely operated vehicle (ROV). Over 60 gravity and piston cores were collected.

Tectonic and sedimentary controls on widespread gas emissions in the Sea of Marmara: Results from systematic, shipborne multibeam echo sounder water column imaging

Understanding of the evolution of fluid-fault interactions during earthquake cycles is a challenge that acoustic gas emission studies can contribute. A survey of the Sea of Marmara using a shipborne, multibeam echo sounder, with water column records, provided an accurate spatial distribution of offshore seeps. Gas emissions are spatially controlled by a combination of factors, including fault and fracture networks in connection to the Main Marmara Fault system and inherited faults, the nature and thickness of sediments (e.g., occurrence of impermeable or gas-bearing sediments and landslides), and the connectivity between the seafloor and gas sources, particularly in relation to the Eocene Thrace Basin. The relationship between seepage and fault activity is not linear, as active faults do not necessarily conduct gas, and scarps corresponding to deactivated fault strands may continue to channel fluids. Within sedimentary basins, gas is not expelled at the seafloor unless faulting, deformation, or erosional processes affect the sediments. On topographic highs, gas flares occur along the main fault scarps but are also associated with sediment deformation. The occurrence of gas emissions appears to be correlated with the distribution of microseismicity. The relative absence of earthquake-induced ground shaking along parts of the Istanbul-Silivri and Princes Islands segments is likely the primary factor responsible for the comparative lack of gas emissions along these fault segments. The spatiotemporal distribution of gas seeps may thus provide a complementary way to constrain earthquake geohazards by focusing the study on some key fault segments, e.g., the northern part of the locked Princes Islands segment.

Neogene Paratethyan Succession in Turkey and Its Implications for the Palaeogeography of the Eastern Paratethys

Abstract The Neogene marginal succession of the Eastern Paratethys (EP) crops out along the southern Black Sea coast and in the Marmara region of Turkey, and provides important clues to the tectono-sedimentary and palaeoceanographic conditions. In the Tarkhanian stage, the southern margin of the EP basin was largely a carbonate platform covered by warm, marine waters. From the end of the Tarkhanian to the Early Chokrakian there was an overall emergence throughout the basin, which is indicated by an influx of siliciclastic sediments. The fossil assemblage indicates that normal marine conditions persisted during most of this period, except for a salinity reduction towards the end due to an eustatic isolation of the basin, which in turn led to anoxic bottom water conditions. The Late Chokrakian isolation became even more severe during the Karaganian as indicated by the endemic fossil assemblage indicating brackish-marine conditions. Carbonate platform conditions prevailed in the northern Pontides during this time. In the Early Konkian, the basin was reconnected briefly with the world ocean by a transgression from the Indo-Pacific Ocean. In the Late Konkian there was a return to brackish-marine conditions. Lower Sarmatian sediments are absent in the southern margin of the EP, but elsewhere in the basin this stage is characterized by a widespread marine transgression. In the Middle-Late Sarmatian, the EP basin was partially isolated with freshening and anoxic bottom-water conditions. During this time there was a brief marine transgression from the Mediterranean into the Marmara region, but it did not reach the Paratethyan basin. The Pontian is characterized by an extensive transgression from the EP that inundated the Marmara and northeastern Aegean regions. The connection with the Marmara Basin was cut off during the Kimmerian and re-established during the Late Akchagylian, when the EP basin was inundated by the Mediterranean waters via the Sea of Marmara as a result of increased North Anatolian Fault activity and a short-term global sea level rise.

Integration of Earth Science Research on the Turkish and Greek 1999 Earthquakes

Preface. In Memoriam: Sirrn Erinc. In Memoriam: Aykut Barka. List of Contributors. Part 1: Turkish 1999 Earthquake. 1. The 17 August 1999 (Golcuk (Kocaeli)-Arifiye (Adapazari) and 12 November 1999 Duzce earthquakes, NW Turkey: their mechanism and tectonic significance E. Gokten, et al. 2. Imaging of the Izmit rupture from the strong motion records M. Bouchon, et al. 3. Tectonic setting of the eastern Marmara Sea B. Alpar, C. Yaltirak. 4. Transition of the North Anatolian Fault Zone (NAZ) in the Sea of Marmara A. Ulugamma, E. Ozel. 5. Western extension of the north Anatolian Fault and associated structures in the Gulf of Saros, NE Aegean Sea M.N. Cagammaatay, et al. 6. Methane in sediments of the deep Marmara Sea and its relation to local tectonic structures P. Halbach, et al. 7. The tsunami threat in the Sea of Marmara, Turkey: A review D.R. Tappin, et al. 8. Earthquakes of the Marmara Sea Basin: Reflections on the need for co-operation between historian and scientist C.F. Finkel. Part 2: Greek 1999 Earthquakes. 9. The Athens earthquake September 7, 1999: Neotectonic regime and geodynamic phenomena I. Mariolakos, I. Fountoulis. 10. Three dimensional P-wave crustal velocity structure beneath Athens region (Greece) using micro-earthquake data G. Drakatos, et al. 11. Earthquake triggering in Greece and the case of the 7 September 1999 Athens Earthquake G.A. Papadopoulos. 12. Destructive earthquake and seismotectonics in the Gulf of Corinth, Central Greece: A Review D. Papanastassiou. 13. Trans-Aegean seismicity, seismic hazard and defences P.W. Burton, G.-A.Tselentis. 14. Methods for imaging earthquake deformation using satellite data and digital elevation models A. Ganas. Subject Index.